The notion of "class" tradionally has been used as a model of conceptual organization and development. On this view, to qualify as an instance of a concept, the object in question has to possess the relevant defining criteria of the class. I have presented an analysis of a type of concept which is not readily characterized by the class model--the collection. A collection is the referent of a collective noun, e.g., forest, family, pile. Collections differ from classes in their part-whole relationships, the internal structure and the nature of the higher order units they form. Support for this analysis comes from previous studies demonstrating the greater psychological integrity of collections and their resulting advantage for holistic processing. The simple relabeling of identical elements as a collection (e.g., forest) or a class (e.g., trees) changes the nature of the organization subjects impose on an array and consequently results in differences in cognitive functioning. These differences appear despite the fact that no literal rearrangement of elements has taken place. The purpose of the proposed studies is to investigate how the collection and class structures are differentially represented and how they affect cognition. More specifically, this work provides a developmental investigation of (a) the nature of the information that is contained in a collections vs. a class representation of an identical array, (b) whether information is differentially encoded or whether a common memorial representation can be differentially processed to yield the obtained collection-class differences, (c) whether the spontaneous organization subjects impose on an array is more similar to a collection or a class representation. Converging evidence on these issues will be obtained from a number of different domains: recognition memory, verbal recall, imagery, number estimation, class inclusion, and concept acquisition. The results of these studies will provide the basis for formulating principles of organization and explaining its role in cognitive functioning.